do u have the card reader and an extra garmin card. Also need the mapsource program to work on computer.I use to have the 172c and had all of that stuff before I upgraded to the 540s.If you dont have these thing it may not be worthwhile to look for them cause these units are quite old.
Excuse me if I don't answer the question right. I'm just trying to help. To enter a waypoint just hit the 'mark' button, then press 'enter'. If you have the coordinates to a location that you aren't, you can do the same, but before you press enter, use the arrow keys to scroll to the lat and lon and change the numbers before you hit enter.